1. Field of the Invention
The present invention relates to a printed wiring board formed by stacking multiple conductor layers through the intermediation of an insulator, a semiconductor package including the printed wiring board, and a printed circuit board including the semiconductor package.
2. Description of the Related Art
In order to realize downsizing and sophistication in functionality of electronic equipment, there is a demand for a printed wiring board having a semiconductor element mounted thereon to have densified wiring and higher circuit operation speed. Due to the demand for the densification, signal wirings of a printed wiring board tend to be closer to each other, and vias for connecting wirings in different wiring layers tend to have smaller diameters and smaller pitches.
In addition, with regard to a printed circuit board in which a semiconductor package is mounted on a motherboard (main board) under a state in which an interposer substrate (printed wiring board) of the semiconductor package and the main board are electrically and physically connected via connection terminals such as solder balls, the connection terminals have smaller pitches. As the distance between wirings becomes smaller due to the densification in this way, crosstalk noise caused by electromagnetic coupling between signal wirings increases.
Further, due to the higher circuit operation speed, the frequency of an electromagnetic field caused by signal transmission becomes higher, and also crosstalk noise caused, by a minute structure is no longer negligible. In particular, crosstalk noise caused at a via or a connection terminal which is wiring orthogonal to the surface of a printed wiring board (in a board thickness direction) is a serious problem although the structure thereof is small compared with a signal wiring pattern formed on the surface of a printed wiring board.
Accordingly, as a method of reducing crosstalk noise caused between wirings extending in the board thickness direction, there is proposed a method in which, between signal vias, an adjacent via at a ground, potential is arranged (see Japanese Patent Application Laid-open No. 2005-340247).
In the conventional structure described above, crosstalk noise caused between signal vias in a printed wiring board among wirings extending in out-of-plane directions can be reduced. However, crosstalk noise caused between connection terminals such as solder for connecting a pad on the printed wiring board and a pad on the main board among wirings extending in out-of-plane directions cannot be reduced. Therefore, such a measure is insufficient as a measure for reducing crosstalk noise between wirings extending in a direction orthogonal to the plane direction.